Waterless electrically operated propellant

ABSTRACT

An electrically operated propellant includes a perchlorate oxidizer and a water insoluble polymeric binder with a water solubility of less than 0.1 grams (g) per 100 grams water at 25° Celsius (° C.). The electrically operated propellant is substantially waterless with a water content of less than 10 weight % (wt. %) water based on total weight of the electrically operated propellant.

BACKGROUND

Missiles and rockets burn propellants within combustion chambers to generate pressurized gases. The pressurized gases are directed through a nozzle to provide thrust and accordingly propel the body of the missile or rocket.

Solid rocket propellants are formed with a solid oxidizer, for instance ammonium perchlorate, fuels, additives, and binders. Ignition systems that elevate the temperature of the solid rocket propellant to the point of combustion are used to ignite the solid rocket fuel.

After ignition of a solid rocket motor, the reaction generally cannot be interrupted until the fuel is completely consumed, and solid rocket propellant burns according to the shape of the propellant grain, the propellant burn rate and its operating pressure, which is dictated by the nozzle throat size. Thus, the burn rate of the fuel proceeds according to a set of predefined parameters that generally cannot be changed during launch and/or flight.

Some solid propellants can be electrically controlled propellants that are ignitable and extinguishable under a variety of conditions, including under high pressures within a rocket motor combustion chamber. Such electrically operated propellants can be selectively ignited and extinguished over a broad range of conditions, which facilitates the selective generation of thrust for a variety of applications, for example, to control to a vehicle without consuming the entirety of the propellant at one time.

SUMMARY

According to embodiments of the present invention, an electrically operated propellant includes a perchlorate oxidizer and a water insoluble polymeric binder with a water solubility of less than 0.1 grams (g) per 100 grams water at 25° Celsius (° C.). The electrically operated propellant is substantially waterless with a water content of less than 10 weight % (wt. %) water based on total weight of the electrically operated propellant.

According to other embodiments of the present invention, an electrically operated propellant includes a perchlorate oxidizer and a water insoluble polymeric binder including a copolymer with a water solubility of less than 0.1 grams (g) per 100 grams water at 25° Celsius (° C.). The electrically operated propellant is substantially waterless with a water content of less than 10 wt. % water based on total weight of the electrically operated propellant.

Yet, according to other embodiments of the present invention, a method of making an electrically operated propellant includes combining a perchlorate oxidizer and a water insoluble polymeric binder with a water solubility of less than 0.1 grams (g) per 100 grams water at 25° Celsius (° C.) to form a propellant composition. The method further includes forming the propellant composition into a solid propellant configuration. The electrically operated propellant is substantially waterless with a water content of less than 10 wt. % water based on total weight of the electrically operated propellant.

Additional features and advantages are realized through the techniques of the present invention. Other embodiments and aspects of the invention are described in detail herein and are considered a part of the claimed invention. For a better understanding of the invention with the advantages and the features, refer to the description and to the drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

For a more complete understanding of this disclosure, reference is now made to the following brief description, taken in connection with the accompanying drawings and detailed description, wherein like reference numerals represent like parts:

FIG. 1 is a cross-sectional view of a gas generation assembly including an electrically operated propellant; and

FIG. 2 is a flow diagram showing a method of making an electrically operated propellant.

DETAILED DESCRIPTION

Electrically operated propellants can be controlled (ignited, extinguished, and throttled) using an electrical signal provided by one or more configured electrodes. For example, applying a voltage across the electrodes ignites the propellant, and conversely, the interrupting the voltage extinguishes the propellant. In a rocket motor, it may be desirable to throttle or interrupt the burn of the electrically operated propellant during vehicle flight in order to control the rocket motor burn during different flight events in order to accomplish a desired mission in a variable environment.

Generally, electrically operated solid propellants include a perchlorate oxidizer, a metal fuel, a polymeric binder, and a solvent. Water has most commonly been used to solubilize the polymeric binder and form an aqueous solution with the additional propellant ingredients.

One challenge of using electrically operated propellants, in a significantly cold space propulsion application scenario, for example, is that the water used to form aqueous solutions can boil, due to the pressure drop, or freeze, due to the low temperatures, if exposed directly to a space environment. Even if the water in the propellant is not directly exposed to the space environment, the included water ingredient poses an overall issue due to the significantly high and/or low temperature and pressure exposure in space. Risks of the water in the electrically operated propellants include potentially rendering the propellant inoperable are therefore undesirable for space applications.

Similarly, the water in electrically operated propellants that are used in other applications, such as in airbag inflators, presents challenges because including volatile components in the formulation that could be labile are problematic. This volatility makes using electrically operated propellants with significant quantities of water challenging, as water content verification and continuous absorption and loss of water despite manufacturing, storage, and use in controlled environments pose additional water related issues.

Additionally, long term storage of an electrically operated propellant with a water ingredient is challenging, as water may interact with other materials, the propellant, rocket motor, and/or flight vehicle. Further, water presents challenges with respect to with propellant relaxation out of the desired propellant shape, oxidation, as well as material compatibility with additional materials used in the rocket motor build.

Accordingly, one or more aspects of the present invention address the above-described shortcomings by providing electrically operated propellants and methods of making and using electrically operated propellants, which are substantially waterless in some embodiments, and waterless in other embodiments. In one or more aspects of the present invention, the electrically operated solid propellants include a perchlorate oxidizer, a metal fuel, and a water insoluble binder(s) (e.g., polymer electrolytes, copolymers, or a combination thereof), which replaces a water-soluble binder. Thus, any aqueous solvents, such as water, which are required for water soluble binders (e.g., casein, methyl cellulose, polyethylene oxide, polyvinyl acetate, and polyvinyl alcohol) are substantially removed or eliminated.

Aspects of the present invention provide various advantages. Water is reduced or completely eliminated in electrically operated propellant compositions by using water insoluble polymeric binder(s), which replace any aqueous solvent polymeric binder system (e.g., casein, methyl cellulose, polyethylene oxide, polyvinyl acetate, and polyvinyl alcohol). The compositions eliminate the risk of water rendering the propellant inoperable when exposed directly or indirectly to a space environment in a space propulsion application (e.g., a rocket motor). Eliminating volatile water allows the electrically operated propellant to be used in other non-space applications where water loss or absorption is undesired, for example, in airbag inflators.

The term “substantially waterless” or “non-aqueous” and variations thereof is used in this detailed description to mean a water content of less than 10 weight % (wt. %) water, less than 5 wt. % water, or less than 0.1 wt. % water. In some aspects, substantially waterless means completely waterless, with 0 wt. % water present in the composition.

The term “free of” and variations thereof when used in reference to a water-soluble polymeric binder, is used in this detailed description to mean 0 wt. %.

The term “water insoluble” and variations thereof is used in this detailed description to mean a water solubility of less than 0.1 grams (g) per 100 grams water at 25° Celsius (° C.).

The term “polymer electrolyte” and variations thereof is used in this detailed description to mean an electrically conducting solution of a salt in a polymer.

Electrically operated propellants described herein include, but are not limited to, a perchlorate oxidizer, a metal fuel, and a water insoluble polymeric binder. Non-limiting examples of perchlorate oxidizers include perchlorate oxidizers such as aluminum perchlorate, ammonium perchlorate, barium perchlorate, calcium perchlorate, lithium perchlorate, magnesium perchlorate, perchlorate acid, strontium perchlorate, sodium perchlorate, or any combination thereof.

The amount of the perchlorate oxidizer present in the electrically operated propellant varies depending on the type of oxidizer and end propellant/application. According to some aspects of the present invention, the electrically operated propellant includes a perchlorate oxidizer in an amount of about 30 to about 90 percent of the total mass of the electrically operated propellant. According to other aspects of the present invention, the electrically operated propellant includes a perchlorate oxidizer in an amount of about 30 to about 65 percent of the total mass of the electrically operated propellant.

The electrically operated propellant further includes, optionally, a metal fuel. The metal fuel assists propellant operation in several ways, including but not limited to facilitating the application of an electrical signal or increasing the density of the propellant. Non-limiting examples of the metal fuel include tungsten, magnesium, copper oxide, copper, titanium, aluminum, or any combination thereof.

The amount of the metal fuel present in the electrically operated propellant varies depending on the type of fuel and end propellant/application. According to some aspects of the present invention, the electrically operated propellant includes a metal fuel in an amount of about 0 to about 40 percent of the total mass of the electrically operated propellant. When included, the electrically operated propellant includes less than 40 percent weight of the total weight of the electrically operated propellant. According to other aspects of the present invention, the electrically operated propellant includes a metal fuel in an amount of about 0 to about 30 percent of the total mass of the electrically operated propellant.

A polymer electrolyte is an electrically conducting solution of a salt in a polymer, or a polymer with charged or chargeable groups when dissolved in a suitable solvent. Solid or gel polymer electrolytes are typically defined as blends containing an electrically conductive polymer, a metal salt, a finely divided inorganic filler material, and a finely divided ion conductor. The polymer electrolyte can be a solid polymer electrolyte, a gel polymer electrolyte, a dry solid polymer electrolyte, or a composite polymer electrolyte.

Solid or gel polymer electrolytes are blends containing an electrically conductive polymer, a metal salt, a finely divided inorganic filler material, and a finely divided ion conductor. For the purposes of this invention, defined in conjunction with polymer electrolytes are conducting polymer composites, which are electrically conducting composites that include a non-conducting polymer matrix and an electrically conducting material, such as metal particles or carbon black.

A non-limiting examples of solid polymer electrolyte formulations include lithium perchlorate, polyethylene oxide, and additional optional additives, which are combined and prepared using a solution casting method, or other similar method. Additional polymer hosts include, but are not limited to, polypropylene oxide, polyacrylonitrile, polyvinylchloride, poly(2-ethyl-2-oxazoline), and polydimethylsiloxane. Additional polymer electrolyte formulation examples include PEO-LiClO₄; PEO-LiBF₄; PEO-Cu(ClO)₂; and PEO-LiCF₃SO₃.

A composite polymer electrolyte is a composite that includes non-conducting polymer matrix and an electrically conducting material, for example, metal particles or carbon black.

The water insoluble polymeric binder also can be a copolymer, such as a copolymer binder system. A non-limiting example of a water insoluble copolymer is polyurethane. In another example, a copolymer of polyvinyl alcohol (PVA) and short chain diols (e.g., (CH₂)_(n)(CH₂OH)₂, n=1-5) is reacted with isocyanate to form a polyurethane.

The amount of the water insoluble polymeric binder present in the electrically operated propellant varies depending on the type of water insoluble polymeric binder and end propellant/application. According to some aspects of the present invention, the electrically operated propellant includes a water insoluble polymeric binder in an amount of about 10 to about 50 percent of the total mass of the electrically operated propellant. According to other aspects of the present invention, the electrically operated propellant includes a water insoluble polymeric binder in an amount of about 15 to about 30 percent of the total mass of the electrically operated propellant.

The electrically operated propellant can be used in a variety of applications, such as a gas generation system of a rocket motor. Other applications for the electrically operated propellant include, but are not limited to, other forms of gas generations systems used in place of traditional solid or liquid rocket motor solutions, such as orbit maintenance systems, divert/attitude control systems, and ignition systems, in additional to as a replacement for traditional and smart air bag inflator systems, as well as ejection systems.

The water insoluble polymeric binder cooperates with the perchlorate oxidizer and the metal fuel to combine these components into a solid fuel propellant shapeable into any configuration such as the cylindrical configurations provided in FIG. 1, which is described in further detail below. The electrically operated propellant has a storage modulus sufficiently high to allow for the maintenance of the shape the propellant is molded into at manufacture. For instance, the electrically operated propellant has a storage modulus of 300 psi or greater at ambient temperature that accordingly allows the propellant in the configurations shown in FIG. 1 or other configurations to maintain its shape through dynamic conditions including, but not limited to, pressurization, launch and flight. The propellant with a consistent shape accordingly maintains a predictable performance profile as the shape and surface area of the propellant are relatively static during operation. The electrically operated propellant is thereby formable (e.g., can be cast or molded) into any number of grain configurations and reliably perform with a desired performance profile (thrust dictated at least in part by the grain surface area) even when subject to dynamic conditions.

FIG. 1 depicts a cross-sectional view of a gas generation assembly including an electrically operated propellant according to aspects of the present invention. It is to be noted that the gas generation system with electrically operated propellant shown in FIG. 1 is but one example, and the electrically operated propellant can be used in other configurations, applications, and gas generation systems.

The gas generation system 100 is shown as part of an overall assembly, such as a rocket motor 102. In one example, the gas generation system 100 includes the rocket motor 102. The gas generation system 100 includes the electrically operated propellant 108, configured to provide thrust through a rocket nozzle 112.

The gas generation system 100 includes a combustion chamber of 104 having the electrically operated propellant 108 positioned therein. Two or more electrodes 110 extend into the electrically operated propellant 108 within the combustion chamber 104. The electrically operated propellant 108 fills a portion of combustion chamber 104 and has a predetermined grain shape. In another example, the electrically operated propellant 108 fills substantially the entirety of the combustion chamber 104. That is to say, the electrically operated propellant 108 extends from the position shown in FIG. 1 toward a position in close proximity to the nozzle 112. Accordingly, the two or more electrodes 110 similarly extend through the electrically operated propellant 108 toward the nozzle 112.

The electrically operated propellant 108 includes a formulation that allows for the igniting and extinguishing of the propellant in a variety of conditions according to the application (and interruption of the application) of electricity through the electrodes 110. For instance, the electrically operated propellant 108 is configured to ignite with the application of voltage across the electrodes 110. Conversely, the electrically operated propellant 108 is extinguished with the interruption of the voltage at a range of pressures (e.g., from 0 psi to 2,000 psi). For instance, where the combustion chamber 104 is part of the rocket motor 102, and the motor is in the process of generating thrust, the pressure within the combustion chamber 104 is greater than 200 psi, for instance from 200 to 2,000 psi. In this condition, it may be desirable to interrupt the burn of the electrically operated propellant 108 (e.g., in order to provide changing levels of thrust for a mission with variable requirements). In such a circumstance the voltage applied across the electrodes 110 is interrupted. Despite the pressurized environment of the combustion chamber 104, subjecting the electrically operated propellant 108 to a pressure greater than 200 psi, for instance pressures approaching 2,000 psi, the interruption of voltage to the electrodes 110 allows the electrically operated propellant 108 to extinguish. With the electrically operated propellant 108 extinguished, the generation of thrust is halted and the propellant is preserved for future use. The gas generation systems 100 is configured for ignition and extinguishing during operation. Importantly, even with ambient or high pressures within the combustion chamber 104, such as atmospheric pressure, pressures greater than 200 psi, 500 psi, 1,000 psi, 1,500 psi and up to 2,000 psi, the electrically operated propellant 108 is extinguished with the interruption of electricity (e.g., voltage or current) applied across the electrodes 110.

FIG. 2 is a flow diagram showing a method 200 of making an electrically operated propellant according to some aspects of the present invention. As shown in box 202, a perchlorate oxidizer, an optional metal fuel, and a water insoluble polymeric binder are combined to form a propellant composition. The metal fuel is optional, and in some embodiments, the metal fuel is not included in the propellant composition. As shown in box 204, any additional formulation components are added into the propellant composition. As shown in box 206, the propellant composition is machine processed for a specified time, under specified conditions (temperature, pressure, machine settings, etc.), depending on the particular propellant and configuration. As shown in box 208, the machine processed composition is formed into a solid propellant configuration. The propellant composition is moldable, extrudable, castable, pressable, or a combination thereof, depending on the application. As shown in box 210, the solid propellant configuration is set for a specified amount of time in a controlled environment (temperature, pressure, humidity, etc.), depending on the particular propellant and application.

Various embodiments of the present invention are described herein with reference to the related drawings. Alternative embodiments can be devised without departing from the scope of this invention. Although various connections and positional relationships (e.g., over, below, adjacent, etc.) are set forth between elements in the following description and in the drawings, persons skilled in the art will recognize that many of the positional relationships described herein are orientation-independent when the described functionality is maintained even though the orientation is changed. These connections and/or positional relationships, unless specified otherwise, can be direct or indirect, and the present invention is not intended to be limiting in this respect. Accordingly, a coupling of entities can refer to either a direct or an indirect coupling, and a positional relationship between entities can be a direct or indirect positional relationship. As an example of an indirect positional relationship, references in the present description to forming layer “A” over layer “B” include situations in which one or more intermediate layers (e.g., layer “C”) is between layer “A” and layer “B” as long as the relevant characteristics and functionalities of layer “A” and layer “B” are not substantially changed by the intermediate layer(s).

The following definitions and abbreviations are to be used for the interpretation of the claims and the specification. As used herein, the terms “comprises,” “comprising,” “includes,” “including,” “has,” “having,” “contains” or “containing,” or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a composition, a mixture, process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but can include other elements not expressly listed or inherent to such composition, mixture, process, method, article, or apparatus.

Additionally, the term “exemplary” is used herein to mean “serving as an example, instance or illustration.” Any embodiment or design described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments or designs. The terms “at least one” and “one or more” are understood to include any integer number greater than or equal to one, i.e. one, two, three, four, etc. The terms “a plurality” are understood to include any integer number greater than or equal to two, i.e. two, three, four, five, etc. The term “connection” can include an indirect “connection” and a direct “connection.”

References in the specification to “one embodiment,” “an embodiment,” “an example embodiment,” etc., indicate that the embodiment described can include a particular feature, structure, or characteristic, but every embodiment may or may not include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

For purposes of the description hereinafter, the terms “upper,” “lower,” “right,” “left,” “vertical,” “horizontal,” “top,” “bottom,” and derivatives thereof shall relate to the described structures and methods, as oriented in the drawing figures. The terms “overlying,” “atop,” “on top,” “positioned on” or “positioned atop” mean that a first element, such as a first structure, is present on a second element, such as a second structure, wherein intervening elements such as an interface structure can be present between the first element and the second element. The term “direct contact” means that a first element, such as a first structure, and a second element, such as a second structure, are connected without any intermediary conducting, insulating or semiconductor layers at the interface of the two elements.

The terms “about,” “substantially,” “approximately,” and variations thereof, are intended to include the degree of error associated with measurement of the particular quantity based upon the equipment available at the time of filing the application. For example, “about” can include a range of ±8% or 5%, or 2% of a given value.

The flowchart and block diagrams in the Figures illustrate possible implementations of fabrication and/or operation methods according to various embodiments of the present invention. Various functions/operations of the method are represented in the flow diagram by blocks. In some alternative implementations, the functions noted in the blocks can occur out of the order noted in the Figures. For example, two blocks shown in succession can, in fact, be executed substantially concurrently, or the blocks can sometimes be executed in the reverse order, depending upon the functionality involved.

The corresponding structures, materials, acts, and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The embodiments were chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.

While the preferred embodiments to the invention have been described, it will be understood that those skilled in the art, both now and in the future, may make various improvements and enhancements which fall within the scope of the claims which follow. These claims should be construed to maintain the proper protection for the invention first described. 

What is claimed is:
 1. An electrically operated propellant comprising: a perchlorate oxidizer; and a water insoluble polymeric binder with a water solubility of less than 0.1 grams (g) per 100 grams water at 25° Celsius (° C.); wherein the electrically operated propellant is substantially waterless with a water content of less than 10 weight % (wt. %) water based on total weight of the electrically operated propellant.
 2. The electrically operated propellant of claim 1, wherein the perchlorate oxidizer is aluminum perchlorate, ammonium perchlorate, barium perchlorate, calcium perchlorate, lithium perchlorate, magnesium perchlorate, perchlorate acid, strontium perchlorate, sodium perchlorate, or any combination thereof.
 3. The electrically operated propellant of claim 1, further comprising a metal fuel.
 4. The electrically operated propellant of claim 1, wherein the water insoluble polymeric binder comprises a polymer electrolyte.
 5. The electrically operated propellant of claim 4, wherein the polymer electrolyte is a solid polymer electrolyte or a gel polymer electrolyte.
 6. The electrically operated propellant of claim 4, wherein the polymer electrolyte is a dry solid polymer electrolyte.
 7. The electrically operated propellant of claim 4, wherein the polymer electrolyte is a conductive polymer composite comprising a non-conducting polymer matrix and an electrically conducting material.
 8. The electrically operated propellant of claim 1, wherein electrically operated propellant is waterless, and the water content is 0 wt. % water.
 9. An electrically operated propellant comprising: a perchlorate oxidizer; and a water insoluble polymeric binder comprising a copolymer with a water solubility of less than 0.1 grams (g) per 100 grams water at 25° Celsius (° C.); wherein the electrically operated propellant is substantially waterless with a water content of less than 10 wt. % water based on total weight of the electrically operated propellant.
 10. The electrically operated propellant of claim 9, wherein the perchlorate oxidizer is aluminum perchlorate, ammonium perchlorate, barium perchlorate, calcium perchlorate, lithium perchlorate, magnesium perchlorate, perchlorate acid, strontium perchlorate, sodium perchlorate, or any combination thereof.
 11. The electrically operated propellant of claim 9, wherein electrically operated propellant is waterless, and the water content is 0 wt. % water.
 12. The electrically operated propellant of claim 9, wherein the copolymer of the water insoluble polymeric binder is a polyurethane.
 13. A method of making an electrically operated propellant, the method comprising: combining a perchlorate oxidizer and a water insoluble polymeric binder with a water solubility of less than 0.1 grams (g) per 100 grams water at 25° Celsius (° C.) to form a propellant composition; and forming the propellant composition into a solid propellant configuration; wherein the electrically operated propellant is substantially waterless with a water content of less than 10 wt. % water based on total weight of the electrically operated propellant.
 14. The method of claim 13, wherein the perchlorate oxidizer is aluminum perchlorate, ammonium perchlorate, barium perchlorate, calcium perchlorate, lithium perchlorate, magnesium perchlorate, perchlorate acid, strontium perchlorate, sodium perchlorate, or any combination thereof.
 15. The method of claim 13, wherein the water insoluble polymeric binder comprises a polymer electrolyte.
 16. The method of claim 15, wherein the polymer electrolyte is a solid polymer electrolyte or a gel polymer electrolyte.
 17. The method of claim 15, wherein the polymer electrolyte is a conductive polymer composite comprising a non-conducting polymer matrix and an electrically conducting material.
 18. The method of claim 13, wherein electrically operated propellant is waterless, and the water content is 0 wt. % water.
 19. The method of claim 13, wherein the water insoluble polymeric binder is a copolymer.
 20. The method of claim 19, wherein the copolymer of the water insoluble polymeric binder is a polyurethane. 